1. Field of the Invention
The present invention relates to a method employing bumping algorithm for estimation of signal frequency, and relates also to a displacement estimation device and a method for the same.
2. Description of the Related Art
As background, the conventional bumping algorithm will first be explained referring to FIG. 1. As shown in the figure, from the perspective of bumping algorithm, a one-dimensional sinusoidal signal includes two states: 0 and 1; and the transition point between these two states is dependent on the bumping threshold. The term “bumping threshold” is a predetermined magnitude counted from a peak downward, or a predetermined magnitude counted from a valley upward. Referring to the figure, although the middle point of the amplitude is at the point A, in order to filter noises so that the signal state will not change due to minor vibrations, the transition point for the signal to change from 1 to 0 is set at the point A1, while the transition point for the signal to change from 0 to 1 is set at the point A2. That is, when the signal passes through a peak, the signal state does not change until the signal further goes through the predetermined magnitude d to reach a point lower than A1, and only after this point it is determined that the signal state changes from 1 to 0; likewise, when the signal passes through a valley, the signal state does not change until the signal further goes through the predetermined magnitude d to reach a point higher than A2, and only after this point it is determined that the signal state changes from 0 to 1.
The bumping algorithm may be applied to, for example, the following application. If one observes a speckle signal on an object from an observation window at a fixed location, the frequency of the signal varies in accordance with the relative movement speed between the surface of the object and the surface of the window. The higher the relative speed is, the higher the frequency of the speckle signal will be; the lower the relative speed is, the lower the frequency of the speckle signal will be. Thus, by sensing the frequency of the speckle signal with a proper optical device, the relative speed may be obtained. The above mentioned bumping algorithm may be used to convert an analog signal to a digital signal, so that the calculation of the relative speed may be easier. Furthermore, by providing two optical signal receivers at two nearby locations along an one-dimensional axis, referring to as the first channel and the second channel, the phase difference between the signals received by the two channels may be used to determine the movement direction of the object in the dimension.
Referring to FIG. 2 in which the horizontal coordinate is time and the vertical coordinate is the received light intensity, and (x1, x2) represents the digital states of the signals received by the first and second channels, as converted by means of the bumping algorithm, it may be seen that (x1, x2) changes from (1,1) to (1,0), and then to (0,0). This shows that the second channel is leading, which means that the object under observation is moving from the second channel (the second optical receiver) to the first channel (the first optical receiver). The movement speed of the object may be calculated by the frequency of the signal state changes.
FIG. 3 shows a conventional device structure for estimating displacement by means of the bumping algorithm. The device includes a signal capturing unit 11 which captures a signal and sends it to a bumping-count displacement estimation unit 15. The bumping-count displacement estimation unit 15 estimates the displacement according to the phase difference between the received signals, and the frequency of the signal state changes (i.e., the bumping count). The estimated displacement is outputted by an estimated displacement output unit 19.
The above mentioned conventional device has a drawback in that, the detected signal intensity and phase may vary due to intensity variation of external light source, noise, and error of the optical device components and the signal may even disappear for a short while. Therefore, to estimate the displacement more precisely, a more sophisticated device is required.